1. Field of the Invention
The present invention relates to a method of testing the cleanness of the inner surfaces of the parts of a fuel injection system and the parts of a fuel pressure accumulating system, both the systems of which constructing a diesel engine fuel injection system and having contacting parts with a fuel, and the parts of the fuel injection system of which being such as a fuel injection pump, fuel injection nozzle, and fuel injection pipe and the parts of the fuel accumulating system of which being such as a common rail, injection pump, injection nozzle, injection pipe, flow limiter, pressure regulator and feed pipe.
2. Description of the Prior Art
Recently, there is an accelerating trend toward an increase in the pressure of fuel to be supplied to a high pressure fuel injection pipe used typically as the parts of a fuel injection system for a diesel engine as a measure for reducing NOx and black smoke, and this has resulted in a need for fuel injection for an injection period of 1 to 2 msec., at a maximum flow rate of 50 m/sec. and at a high internal pressure in the range from 60 to 1500 bar (peak value).
Such a change in market demands is accompanied by an increased possibility of clogging of an injection nozzle caused by foreign particles such as metal particles which have stuck to the inner surface of a high-pressure fuel injection pipe after floating in the air or entering from the outside, and this can cause a faulty operation of a diesel engine or damage to a fuel pump. Thus, it is an important problem to be solved to improve the cleanness of the inner surface of a high-pressure fuel injection pipe in order to prevent this.
In order to improve the cleanness of the inner surface of a high-pressure fuel injection pipe, however, it is necessary to first establish a method of measurement which makes it possible to properly determine the level of cleanness of a product. Under such circumstances, various methods of testing the cleanness of the inner surface of a high-pressure fuel injection pipe such as methods using a injection pump, hand tester methods, syringe and improved syringe have been proposed by the Society of Automotive Engineers, foreign manufacturers and ISO committees.
However, among the testing methods proposed in the past, both of the injection pump method and hand tester method are unsuitable for the evaluation of a high quality high-pressure fuel injection pipe belonging to the P-class or higher which inherently has less foreign particles because such methods are vulnerable to noises from a pump or nozzle. Further, both of the syringe method and improved syringe method have had a problem in that the extraction of foreign particles present in a high-pressure fuel injection pipe tends to be unsatisfactory, although there is less noise from the measuring system.
Thus, test results obtained according to the testing methods proposed in the past have a low level of reproducibility and also includes variation. As a result, no particular method has been established and put in use yet.